This invention relates to faulted current indicators, and particularly to fault indicators which can accommodate themselves to wide variations of load conditions in a distribution network.
A conventional fault indicator indicates the passage of power cable current above a predetermined magnitude, i.e. trip current. The fault indicator's trip current is selected to be greater than the expected current at the installation site. Proper selection of the trip current magnitude is very important for the proper application of fault indicators. Typically, the trip current is selected about two to three times the maximum load current and less than one half the available fault current. This method of application provides a good trade off between maximum sensitivity while minimizing the un-wanted trips by periodic overloads.
Applying conventional fault indicators in a large distribution network often requires many fault indicators with different trip currents to coordinate with loading variations within the network. In addition to the cost of stocking many different fault indicators, the chance of missapplication also increases.